Patients who need routine surgery are more likely to die if they have their operation towards the end of the week, according to a new study.

Results from the first analysis of its kind shows that patients who have planned surgery on a Friday are 44% more likely to die than those who have their operation on a Monday.

Researchers found that the risk of dying was higher still if the operation was carried out at the weekend.

They found an 82% increased risk if that operation was carried out at the weekend compared to a Monday but stressed that the vast majority of elective procedures are carried out during the working week.

Researchers from the health analyst group Dr Foster Intelligence, which is part of Imperial College London, blame the higher mortality rate for those having operations late in the week on lower standards of care in hospital over the weekend, when patients are recovering.

Dr Paul Aylin, who led the research, told Sky News: "The 48 hours from having an operation are the most critical in terms of developing complications.

"What we expected to find was that as your post-operative period overlapped with the weekend, if there were differences in the quality of care offered, you would see an increase in mortality. And that is what we find."

The researchers looked at more than four million operations carried out in NHS hospitals in England between 2008 and 2011.

Previous research has found worse outcomes for patients admitted to hospital as an emergency at the weekend.

But the new research by the Dr Foster research unit found an even stronger 'weekday effect' on planned procedures.

NHS England is currently reviewing ways of increasing the quality of care available at weekends.

Prof Sir Bruce Keogh, National Medical Director, said: "NHS England is committed to providing safe care for all patients, regardless of when they receive their treatment.

"Our aim is to promote a comprehensive health service, increasing access to the right treatment and co-ordinating care around the needs, convenience and choices of patients, their carers and their families."